THE PRIMITIVE KIDNEYS. 405 



coiled or looped form, are called " coiled canals." To the 

 primary, external aperture in the outer skin, originally 

 alone present, a secondary, internal aperture into the body- 

 cavity (cceloma) is now added. This opening is provided 

 with vibratory cilia, and is thus enabled to absorb the 

 secretional juices from the body -cavity and to discharge 

 them from the body. Now in these Worms also the sexual 

 cells, which develop in the simplest form upon the inner 

 surface of the abdominal wall, pass, when mature, into the 

 coelom, are drawn into the internal, funnel-shaped ciliated 

 openings of the kidney canals, and are carried out of the 

 body with the urine. Thus the urine-forming "coiled 

 canals," or " primitive kidneys," serve, in the female Ringed 

 Worms, as "oviducts," and, in the male, as "sperm-ducts." 



It would of course be most interesting to know the 

 condition, on this point, of the Amphioxus, which, standing 

 midway between Worms and Vertebrates, affords us so 

 much valuable information. Unfortunately this animal, 

 for the present, affords no solution of this matter. At 

 present we know nothing certainly as to the relation 

 between the urinary and the sexual organs of the Amphi- 

 oxus. Some zoologists assert that this animal has no 

 kidneys ; others regard the two long " side canals " as 

 atrophied primitive kidney ducts (Fig. 152, S, vol. i. p. 423) ; 

 yet others consider certain glandular epidermis-swellings on 

 the inner surface of the gill-cavity to'be rudimentary kidneys. 

 Most probably, a great reversion has affected the original 

 primitive kidney canals in the Amphioxus, amounting per- 

 haps to their entire phylogenetic loss. 



Very interesting inferences may be drawn from the 

 Vertebrates of the next stage — the Monorhina, or Cycles- 



